1. Field of the Invention
The present invention relates to an imaging apparatus and a flicker reduction method.
2. Description of Related Art
Japanese Unexamined Patent Application Publication No. 2004-222228 and International Patent Publication No. WO2010/058567 disclose a reduction method of CMOS (Complementary Metal Oxide Semiconductor) flicker. In the flicker reduction method of Japanese Unexamined Patent Application Publication No. 2004-222228, a flicker reduction unit calculates an average value of integrated values of three consecutive fields and normalizes the integrated values by the average value. Then, the flicker reduction unit performs DFT (Discrete Fourier Transform) on the normalized integrated value. The flicker reduction unit estimates a flicker coefficient from a spectrum extracted by DFT and reduces flicker.
In International Patent Publication No. WO2010/058567, an acquisition unit acquires a line integrated value of some of the horizontal lines among horizontal lines constituting one frame. Further, a memory stores the acquired line integration values of a plurality of screens. A flicker extraction unit performs DFT on the line integration value sequence of a plurality of screens and extracts information of a flicker component.
However, in Japanese Unexamined Patent Application Publication No. 2004-222228, a flicker reduction circuit performs DFT processing on signals of one frame. If there is a moving object in a subject, a correction gain rapidly changes, and thus appropriate correction cannot be performed, likely causing destruction of a video. Further, as the DFT processing is performed inside a frame, when there is no flicker component for one cycle inside one frame, it may not be possible to detect flicker in, for example, a high-speed imaging mode.
In International Patent Publication No. WO2010/058567, since normalization unlike Japanese Unexamined Patent Application Publication No. 2004-222228 is not performed, a DC component in a video is not removed. Therefore, as a flicker component detected by brightness of a subject differs even under the same flicker environment, appropriate correction may not be performed. Further, when there is a moving object in the subject, a flicker component acquired by inter-frame DFT processing rapidly changes. Accordingly, appropriate correction cannot be performed, likely causing destruction of a video.
The present invention has been made in light of the above-described points and an object of the present invention is to provide an imaging apparatus and a flicker reduction method that can appropriately reduce flicker.